You can ask PHP to show error messages. Go to "c:\Program Files\IIS Express\PHP\v5.3\" (where v5.3 is your current version) and rename "php.ini-development" to "php.ini". The original "php.ini" go to be deleted in fact, you can rescue this before.

It will show reason of fail and string number in your browser. In Webmatrix you can use "show string numbers" and "go to string".